The veterinary studies area conducts epidemiologic investigations using data compiled by North American veterinary university teaching facilities, the Armed Forces Institute of Pathology, the Department of Defense Military Working Dog Agency, NCI's Registry of Experimental Cancers, and other sources when available. These investigations evaluate the role that environmental factors have in the etiology of cancer in animals, particularly to identify situations where the companion domestic animal may serve as a sentinel for human exposures to environmental carcinogens. Major areas of current interest are the necropsy findings among military working dogs who served in Vietnam, 1968-1973, household and lawn chemical exposures of pet dogs diagnosed with malignant lymphoma, and similar chemical exposures of pet dogs diagnosed with cancer of the lower urinary tract. A case-control study comparing the neoplasm experience at necropsy of 1,200 Vietnam service military working dogs compared with those that served in the U.S. found that Vietnam service dogs had a significant twofold excess of testicular seminoma. Examination of military service records showed an excess risk for seminoma among military working dogs that died in Okinawa as significantly associated with prior service in Vietnam. In an independent investigation, analysis of data from 137 cases of human testicular cancer and 130 controls born prior to 1955 revealed a significant, twofold greater risk of testicular cancer in Vietnam veterans. A case-control study of 491 pet dogs with malignant lymphoma found a significant 1.3-fold association with owner use of phenoxy herbicides and/or employment of commercial lawn care companies. A case-control study of 85 pet dogs with cancer of the lower urinary tract found significant associations with owner use of lawn insecticides and professional lawn care companies, and professional grooming plus exposure to flea and tick dips.